Control of flow and/or pressure provided by breathing apparatus

ABSTRACT

The invention comprises a method of operating a breathing apparatus comprising measuring a baseline breath flow parameter being respiratory rate and/or tidal volume or a parameter derived therefrom, varying the flow rate provided by the breathing apparatus, measuring a current breath flow parameter being respiratory rate and/or tidal volume or a parameter derived therefrom, comparing the baseline and current breath flow parameters, and altering operation of the breathing apparatus based on the comparison. The invention also comprises a breathing apparatus that implements the above method.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a breathing apparatus including but notsolely limited to breathing apparatus providing pressure therapy (suchas PAP machines or similar) for treating obstructive sleep apnea and/orbreathing apparatus providing flow and/or nasal high flow (NHF) therapyfor various respiratory disorders.

Description of the Related Art

Breathing apparatus exist that provide flow and/or pressure therapy to apatient.

A certain level of flow and/or pressure are usually desired to provideeffective therapy. However, a flow or pressure that is too high canproduce undesirable effects in a patient that is awake.

It is an object of the present invention to alter the flow and/orpressure provided to a patient by a breathing apparatus dependent onwhether they are awake or asleep and/or based on the reaction of breathflow parameters to changes in flow, or to overcome at least some of thedrawbacks mentioned above.

SUMMARY OF THE INVENTION

In one aspect the present invention may be said to consist in a methodof operating a breathing apparatus comprising the steps of providingfluid to a patient at a flow rate, measuring a current breath flowparameter of a patient, the breath flow parameter comprising respiratoryrate and/or tidal volume, or one or more parameters derived therefrom,comparing the current breath flow parameter to an equivalent baselinebreath flow parameter of the patient measured previously at a differentbaseline flow rate, altering operation of the breathing apparatus basedon the comparison.

Preferably, the method further comprises determining a sleep state of apatient based on the comparison between the current and previous breathflow parameters, wherein altering operation of the breathing apparatusbased on the comparison utilises the determination of sleep state.

Preferably the method further comprises the step of, prior to measuringa current breath flow parameter of a patient, increasing, decreasing ormaintaining the flow rate of the fluid provided to the patient such thatthe flow rate is higher than the baseline flow rate.

Preferably the method further comprises the step of, prior to measuringa current breath flow parameter of a patient, increasing, decreasing ormaintaining the flow rate of the fluid provided to the patient such thatthe flow rate is lower than the baseline flow rate.

Preferably the baseline breath flow parameter is measured during acalibration process.

Preferably wherein the baseline breath flow parameter is measured duringactual use of the breathing apparatus.

Preferably if the sleep state of a patient cannot be determined thencurrent breath flow parameter becomes a baseline breath flow parameter.

Preferably the method further comprises after the current breath flowparameter becomes the baseline breath flow parameter, measuring acurrent breath flow parameter of a patient, the breath flow parametercomprising respiratory rate and/or tidal volume, or one or moreparameters derived therefrom, comparing the current breath flowparameter to the baseline breath flow parameter of the patient measuredpreviously at a different baseline flow rate, altering operation of thebreathing apparatus based on the comparison.

Preferably the flow rate of the fluid provided to the patient isincreased, decreased or maintained but is above the baseline flow rate,the current breath flow parameter is a current respiratory rate and/orcurrent tidal volume, the baseline breath flow parameter is a baselinerespiratory rate and/or baseline tidal volume, and an awake sleep stateis determined if the current respiratory rate is lower than the baselinerespiratory rate, and/or the current tidal volume is higher than thebaseline tidal volume.

Preferably the flow rate of the fluid provided to the patient isincreased, or decreased or maintained but is above the baseline flowrate, the current breath flow parameter is a current respiratory rateand/or current tidal volume, the baseline breath flow parameter is abaseline respiratory rate and/or baseline tidal volume, and an asleepsleep state is determined if the current respiratory rate is the same asor slightly lower than the baseline respiratory rate, and/or the currenttidal volume is lower than the baseline tidal volume.

Preferably the flow rate of the fluid provided to the patient isincreased, decreased or maintained but is below the baseline flow rate,the current breath flow parameter is a current respiratory rate and/orcurrent tidal volume, the baseline breath flow parameter is a baselinerespiratory rate and/or baseline tidal volume, and an awake sleep stateis determined if the current respiratory rate is higher than thebaseline respiratory rate, and/or the current tidal volume is lower thanthe baseline tidal volume.

Preferably the flow rate of the fluid provided to the patient isincrease, decreased or maintained but is below the baseline flow rate,the current breath flow parameter is a current respiratory rate and/orcurrent tidal volume, the baseline breath flow parameter is a baselinerespiratory rate and/or baseline tidal volume, and an asleep sleep stateis determined if the current respiratory rate is the same as or slightlyhigher than the baseline respiratory rate, and/or the current tidalvolume is higher than the baseline tidal volume.

Preferably altering operation of the breathing apparatus comprisesincreasing or decreasing or maintaining the flow rate provided to thepatient, preferably based on the determined sleep state.

Preferably the method comprises increasing the flow rate provided to thepatient if an asleep sleep state is determined, or decreasing the flowrate provided to the patient if an awake sleep state is determined.

Preferably measuring the current breath flow parameter to compare itagainst a baseline breath flow parameter is triggered by one or more of:time, patient physiology.

Preferably the flow rate at which the fluid is provided to a patient isprovided at a fixed or varying flow rate during a breath cycle.

Preferably the fluid is provided to a patient through a patientinterface with at least one nasal prong to provide air into the deadspace.

In another aspect the present invention may be said to consist in abreathing apparatus to provide fluid flow to a patient comprising ablower, at least one sensor, and a controller configured to operate theblower to generate fluid flow at a flow rate to provide to a patient,measure using the sensor a current breath flow parameter of a patientusing the breathing apparatus, the breath flow parameter comprisingrespiratory rate and/or tidal volume, or one or more parameters derivedtherefrom, compare the current breath flow parameter to an equivalentbaseline breath flow parameter of the patient measured previously at adifferent baseline flow rate, alter operation of the breathing apparatusbased on the comparison.

Preferably the controller is further configured to determine a sleepstate of a patient based on the comparison between the current andprevious breath flow parameters, wherein altering operation of thebreathing apparatus based on the comparison utilises the determinationof sleep state.

Preferably the controller is further configured to, prior to measuring acurrent breath flow parameter of a patient, increase, maintain ordecrease the flow rate of the fluid provided to the patient such thatthe flow rate is higher than the baseline flow rate.

Preferably the controller is further configured to, prior to measuring acurrent breath flow parameter of a patient, increase, maintain ordecrease the flow rate of the fluid provided to the patient such thatthe flow rate is lower than the baseline flow rate.

Preferably the baseline breath flow parameter is measured during acalibration process.

Preferably the baseline breath flow parameter is measured during actualuse of the breathing apparatus.

Preferably if the sleep state of a patient cannot be determined thecurrent breath flow parameter becomes a baseline breath flow parameter.

Preferably the controller is further configured to, after the currentbreath flow parameter becomes the baseline breath flow parameter,measure a current breath flow parameter of a patient, the breath flowparameter comprising respiratory rate and/or tidal volume, or one ormore parameters derived therefrom, compare the current breath flowparameter to the baseline breath flow parameter of the patient measuredpreviously at a different baseline flow rate, alter operation of thebreathing apparatus based on the comparison.

Preferably the current breath flow parameter is a current respiratoryrate and/or current tidal volume, the baseline breath flow parameter isa baseline respiratory rate and/or baseline tidal volume, and thecontroller is configured to operate the blower so that the flow rate ofthe fluid provided to the patient is increased, decreased or maintainedbut is above the baseline flow rate, and determine an awake sleep stateif the current respiratory rate is lower than the baseline respiratoryrate, and/or the current tidal volume is higher than the baseline tidalvolume.

Preferably the current breath flow parameter is a current respiratoryrate and/or current tidal volume, the baseline breath flow parameter isa baseline respiratory rate and/or baseline tidal volume, and thecontroller is configured to operate the blower so that the flow rate ofthe fluid provided to the patient is increased, or decreased ormaintained but is above the baseline flow rate, and determine an asleepsleep state if the current respiratory rate is the same as or slightlylower than the baseline respiratory rate, and/or the current tidalvolume is lower than the baseline tidal volume.

Preferably the current breath flow parameter is a current respiratoryrate and/or current tidal volume, the baseline breath flow parameter isa baseline respiratory rate and/or baseline tidal volume, and thecontroller is configured to operate the blower so that the flow rate ofthe fluid provided to the patient is increased, decreased or maintainedbut is below the baseline flow rate, determine an awake sleep state ifthe current respiratory rate is higher than the baseline respiratoryrate, and/or the current tidal volume is lower than the baseline tidalvolume.

Preferably the flow rate of the fluid provided to the patient isincrease, decreased or maintained but is below the baseline flow rate,the current breath flow parameter is a current respiratory rate and/orcurrent tidal volume, the baseline breath flow parameter is a baselinerespiratory rate and/or baseline tidal volume, and the controller isconfigure to determine an asleep sleep state if the current respiratoryrate is the same as or slightly higher than the baseline respiratoryrate, and/or the current tidal volume is higher than the baseline tidalvolume.

Preferably altering operation of the breathing apparatus comprises thecontroller operating the blower to increase or decrease the flow rateprovided to the patient, preferably based on the determined sleep state.

Preferably the controller operating the blower is configured to increasethe flow rate provided to the patient if an asleep sleep state isdetermined, or decrease the flow rate provided to the patient if anawake sleep state is determined.

Preferably measuring the current breath flow parameter to compare itagainst a baseline breath flow parameter is triggered by one or more oftime patient physiology.

Preferably the flow rate at which the fluid is provided to a patient isprovided at a fixed or varying flow rate during a breath cycle.

Preferably the fluid is provided to a patient through a patientinterface with at least one nasal prong to provide air into the deadspace.

In one aspect the present invention may be said to consist in a methodof operating a breathing apparatus to provide therapy to a patientcomprising the steps of: providing fluid to a patient at a nominal flowrate, increasing the flow rate of the fluid provided to the patient,determining a sleep/awake state of the patient from the respiratory rateand/or tidal volume at the first flow rate, if the patient is asleep,providing an fluid flow rate to the patient higher than the nominal flowrate.

Preferably increasing the fluid flow rate comprises: increasing thefluid flow rate to a fixed higher flow rate than the nominal flow rate,or ramping the fluid flow rate at a first ramp rate.

Preferably providing a fluid flow rate to the patient higher than thenominal flow rate comprises: increasing the fluid flow rate to a fixedhigher flow rate than the nominal flow rate, or ramping the fluid flowrate at a second ramp rate higher than the first ramp rate.

Preferably onset of the awake/sleep state is determined by: comparingthe respiratory rate and/or tidal volume to a baseline respiratory rateand/or tidal volume, wherein: an decrease in respiratory rate and/orincrease in tidal volume against the baseline indicates an awake state,no change in the respiratory rate and/or a decrease in tidal volumeagainst the base line indicates a sleep state.

In another aspect the present invention may be said to consist in abreathing apparatus to provide therapy to a patient comprising a flowgenerator and optionally a humidifier operated by a controller fordelivering fluid flow to a patient, the controller for operating theapparatus to: provide fluid to a patient at a nominal flow rate,increase the flow rate of the fluid provided to the patient, determine asleep/awake state of the patient from the respiratory rate and/or tidalvolume at the first flow rate, if the patient is asleep, provide anfluid flow rate to the patient higher than the nominal flow rate.

Preferably increasing the fluid flow rate comprises: increasing thefluid flow rate to a fixed higher flow rate than the nominal flow rate,or ramping the fluid flow rate at a first ramp rate.

Preferably providing a fluid flow rate to the patient higher than thenominal flow rate comprises: increasing the fluid flow rate to a fixedhigher flow rate than the nominal flow rate, or ramping the fluid flowrate at a second ramp rate higher than the first ramp rate.

Preferably onset the awake/sleep state is determined by: comparing therespiratory rate and/or tidal volume to a baseline respiratory rateand/or tidal volume, wherein: a decrease in respiratory rate and/orincrease in tidal volume against the baseline indicates an awake state,no change in the respiratory rate and/or a decrease in tidal volumeagainst the base line indicates a sleep state.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described with referenceto the following drawings of which:

FIG. 1a shows a flow therapy breathing apparatus,

FIG. 1b shows in schematic form the components of the breathingapparatus in FIG. 1,

FIG. 2 shows a high flow breathing apparatus with the humidifierremoved,

FIG. 3 shows a breathing apparatus for providing pressure therapy,

FIG. 4 shows the breathing apparatus with a humidifier in more detail,

FIGS. 5a, 5b shows flow diagrams indicating a method of operating abreathing apparatus according to the invention,

FIG. 6 shows a flow diagram of a method of detecting sleep for thepurpose of operating a breathing apparatus according to the flow diagramin FIG. 5 a,

FIG. 7 shows a baseline respiratory rate and tidal volume of a patientat nominal flow rate,

FIGS. 8a, 8c show respiratory rate and tidal volume of an awake patientwhen flow rates of 15 litres per minute, 30 litres per minute and 45litres per minute are provided by the breathing apparatus,

FIGS. 8b, 8d show respiratory rate and tidal volume of an asleep patientwhen flow rates of 15 litres per minute and 45 litres per minute areprovided by the breathing apparatus,

FIGS. 9A to 9F show the change in respiratory rate and tidal volume forawake patients when high flow is provided at various flow rates,

FIGS. 10A to 10F show a change in respiratory rate and title volume whenhigh pressure is provided for awake and asleep patients.

FIG. 11 shows a possible sleep/awake state detection process.

FIGS. 12a to 12c show flow traces of example detection events andresulting flow variations during operation of a breathing apparatus.

FIG. 13 shows other possible patient interfaces that could be used inthe invention.

FIG. 14 shows the change in various breathing parameters when flow isvaried when the patient is awake and asleep.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the present specification, breathing apparatus (also termed breathsystem or respiratory assistance apparatus/system) can mean among otherthings an apparatus for providing flow therapy or an apparatus forproviding pressure therapy.

Brief Description of Breathing Apparatus

Breathing apparatus for providing humidified and heated gases to apatient (either as flow or pressure therapy for example as CPAP fortreating OSA or flow therapy for treating chronic respiratory disorders)for therapeutic purposes are well known in the art. Systems forproviding therapy of this type (for example respiratory humidification)typically have a structure where gases are delivered to a humidifierchamber from a gases source, such as a blower (also known as acompressor, an assisted breathing unit, a fan unit, a flow generator ora pressure generator). A controller (processor) controls operation ofthe apparatus. It can have access to an internal or external memory thatstores instructions and/or data. As the gases (fluid) pass over the hotwater, or through the heated and humidified air in the humidifierchamber, they become saturated with water vapour. The heated andhumidified gases are then delivered to a user or patient downstream fromthe humidifier chamber, via a gases conduit and a user interface. Abreathing apparatus to provide flow therapy controls the flow rate ofair/oxygen to the patient. A breathing apparatus to provide pressuretherapy controls the pressure provided to the patient.

FIGS. 1a, 1b and 2 show a breathing apparatus for providing flow therapyand/or humidification therapy for treating respiratory disorders. In oneform, such breathing apparatus can be modular and comprise a humidifierunit and a blower unit that are separate (modular) items. The modulesare connected in series via connection conduits to allow gases to passfrom the blower unit to the humidifier unit. In another embodiment, theblower unit and humidifier unit are integrated (“integrated unit”). Ineither case, a flow of air (and optionally oxygen) (more generally“fluid flow”) is provided by a blower unit through a humidificationchamber and then through a conduit and patient interface so that thehumidified flow is provided to a patient.

FIGS. 1a, 1b and show a schematic view of an integrated unit. A user 1receives a stream of heated and humidified air/oxygen (fluid) 11 from abreathing apparatus 10. Air/oxygen flow is provided from blower unit 2 avia a connector conduit 10 to a humidifier chamber 4 a. The stream ofhumidified and heated air exits the humidification chamber 4 a via auser conduit 3, and is provided to the patient or user 1 via a userinterface 5. The process is controlled by a controller 12, whichincludes operating the blower to provide the required flow rate of air,operating the humidifier to create the required humidity and/or anyother operations. The controller can control the blower to provide fluidflow at a fixed or varying rate during the breathing cycle. Theapparatus can also have sensors 13 a, 13 b, such as pressure and/or flowsensors for detecting operation of the apparatus and breathing of thepatient. These can be on the apparatus itself or on the user (patient)interface or both. If on the interface, they can be in any suitablelocation such as on nasal prongs. These sensors can be used (among otherthings) to measure or determine respiratory rate and/or tidal volume ofbreath or parameters derived therefrom. The controller can controloperations of the respective breathing apparatus including fan speed,humidification and other operations of the breathing apparatus such ascontrol based on feedback from sensors 13 a, 13 b and recordal ofcompliance or other operation or sensor data onto a memory 14.

The chamber can be slid on and off. FIG. 2 shows the humidifier chamberremoved, exposing a heater place 20 and the inlet 6 and outlet 3 to/fromthe humidifier chamber. User controls 22 and user I/O 21 are also shown.

The user interface 5 shown in FIGS. 1a, 1b a nasal cannula and nasalmask respectively, by way of example. However, it should be noted thatin systems of these types, a mask that covers the mouth and nose, afull-face mask, a nasal pillow mask, or any other suitable userinterface could be substituted for the nasal mask shown. A mouth-onlyinterface or oral mask, or a combination of cannula with anasal/oral/full face mask could also be used. A hybrid mask 132 with aface mask and one or more nasal prongs 133 could be used also (see e.g.FIG. 13), or any other NHF or other interface that provides one or moreprongs for jetting air. FIG. 13 also shows a patient interface 131 thathas prongs 130. Sensors can be placed in or near the prongs to measurebreathing parameters. Also, the patient or user end of the conduit canbe connected to a tracheostomy fitting, or an endotracheal intubation.Examples of other masks are shown in FIG. 13, although these areexemplary only and not limiting. Having at least one nasal prong isparticular useful although not necessarily essential for directing airinto the nasal cavity to clear the dead space. This mechanism is usefulfor the invention as described later. Note, the term breathing apparatusis understood to refer to an apparatus (blower and/or humidifier andassociated components) with or without a patient interface connected tothe apparatus.

For these integrated systems, the most common mode of operation ascontrolled by the controller is as follows: air is drawn by the blower 2a through an inlet into the casing which surrounds and encloses at leastthe blower portion of the system. The blower generates an air streamfrom the flow generator outlet and passes this into the humidifierchamber 4 a. The air stream is heated and humidified in the humidifierchamber, and exits the humidifier chamber via an outlet 3. A flexiblehose or conduit 3 is connected either directly or indirectly to thehumidifier outlet, and the heated, humidified gases are passed to a user1 via the conduit. This is shown schematically in FIG. 2.

In both modular and integrated systems, the gases provided by the blowerunit are generally sourced from the surrounding atmosphere. However,some forms of these systems may be configured to allow a supplementarygas (e.g. oxygen) to be blended with the atmospheric air for particulartherapies. In such systems, a gases conduit supplying the supplementalgas is typically either connected directly to the humidifier chamber orelsewhere on the high pressure (flow outlet) side of the blower unit, oralternatively to the inlet side of the blower unit as described in WO2007/004898. This type of respiratory assistance system is generallyused where a patient or user requires oxygen therapy, with the oxygenbeing supplied from a central gases source. The oxygen from the gasessource is blended with the atmospheric air to increase the oxygenfraction before delivery to the patient. Such systems enable oxygentherapy to be combined with high flow humidification therapy for thetreatment of diseases such as COPD. In such therapies, the oxygenfraction being delivered to the patient be known and controlled. Theoxygen fraction being delivered to the patient can be manuallycalculated or estimated based on a printed look-up table that sets outvarious oxygen fractions that have been pre-calculated based on a rangeof oxygen flow rates supplied from the central gas source and a range offlow rates generated by the blower unit. Alternatively, the oxygenfraction can be measured with an oxygen sensor as described in theco-pending 61/620595.

FIGS. 3 and 4 show a breathing apparatus providing pressure therapy(such as CPAP) to treat OSA or similar. In one form, such a breathingapparatus can be modular that comprise a humidifier unit and a blowerunit that are separate (modular) items. In another embodiment, theblower unit and humidifier unit are integrated (“integrated unit”). Ineither case, pressure is provided by a blower unit through ahumidification chamber and then through a conduit and patient interfaceso that the humidified pressure is provided to a patient.

For example, FIG. 3 shows an integrated breathing apparatus forproviding pressure therapy, e.g. a CPAP apparatus. FIG. 4 shows thecomponents in schematic form of the integrated unit. The blower unit 2 aand the humidifier unit 4 a are contained within the same housing. Atypical integrated system consists of a main blower unit 2 a or assistedbreathing unit that provides a pressurised gases flow, and a humidifierunit 4 a that mates with or is otherwise rigidly connected to the blowerunit. For example, the humidifier unit is mated to the blower unit byslide-on or push connection, which ensures that the humidifier unit isrigidly connected to and held firmly in place on the main blower unit.Referring to FIG. 4, a user 1 receives a stream of heated and humidifiedair from a modular respiratory assistance system. Pressurised air isprovided from an assisted breathing unit or blower unit 2 a via aconnector conduit to the humidifier chamber 4 a. A controller 12 isprovided to control operation of the apparatus. The stream ofhumidified, heated and pressurised air exits the humidification chamber4 a via a user conduit 3, and is provided to the patient or user 1 via auser interface 5. The apparatus can also have sensors 13 a, 13 b, suchas pressure and/or flow sensors for detecting operation of the apparatusand breathing of the patient. These can be on the apparatus itself or onthe user (patient) interface. If on the interface, they can be in anysuitable location such as on nasal prongs. These sensors can be used(among other things) to measure or determine respiratory rate and/ortidal volume of breath or parameters derived therefrom. The controllercan control operations of the respective breathing apparatus includingfan speed, humidification and other operations of the breathingapparatus such as control based on feedback from sensor and recordal ofcompliance or other operation or sensor data onto a memory 14.

U.S. Pat. No. 7,111,624 includes a detailed description of an integratedsystem. A ‘slide-on’ water chamber is connected to a blower unit in use.A variation of this design is a slide-on or clip-on design where thechamber is enclosed inside a portion of the integrated unit in use. Anexample of this type of design is shown in WO 2004/112873, whichdescribes a blower, or flow generator, and an associated humidifier.

Description of Operation

In a breathing apparatus that provides a flow therapy (usually NHF),generally the higher the flow rate of the air/oxygen provided to thepatient, the better the therapy that is provided to them. However, whilea patient is awake providing a flow rate that is too high can beuncomfortable for the patient. Also it causes turbulence in the noseduring expiration, which is noisy and can prevent them from sleeping.While asleep, generally it is desirable to have a higher flow rate toimprove CO₂ washout and also to lower the chance of obstructive eventsduring sleep. Generally, in traditional flow therapy, a rate is set thatwill provide the required level of therapy, typically 10-60 Litres/min,while a keeping the flow rate as low as possible to reduce theundesirable effects, taking into account the desired awake and sleeprequirements. Notwithstanding the above, in other cases, upon detectingthat the patient has gone to sleep or alternatively woken up it may bedesirable to vary the flow rate in some manner (e.g. by ramping at iteither up or down) that is appropriate to provide a flow rate that willassist the patient in the current detected sleep/awake state. Therefore,in general terms it is desirable to vary the flow rate (or otheroperations of the breathing apparatus) provided to the patient based ontheir awake/asleep state or the change of that state.

The present invention relates to an apparatus and method of control thatdetects whether a patient is awake or asleep and changes therapy modeaccording to the sleep state. By way of an example, the apparatuscontrols the flow rate, temperature, humidity, or air/oxygen fraction tothe patient according to their sleep state and the desired flow for suchstates. In an embodiment of the present invention, the apparatus iscontrolled to keep flow rate lower while the patient is awake, andhigher while they are asleep. Other flow variations can be provided alsodepending on the sleep stage and breathing pattern. In general terms,the controller is programmed in a manner to be described below to carryout the detection of when a patient using the breathing apparatus isawake or asleep, and to change operation (e.g. flow rate, temperature,02 fraction delivered) of the breathing apparatus based on whether apatient is awake or asleep.

In general terms, in accordance with the present specification, low flowair/oxygen rate (termed “low flow”) can be considered anything that isnot “high flow”. A high flow air/oxygen rate (“high flow”) can beconsidered any flow rate where heating and/or humidification arerequired for comfort and/or therapy. The transition between high flowand low flow could be anywhere between 0-60 liters per minute, dependingon the application. For example, for children, a high flow might beconsidered to start at as low as 1-2 litres per minute. These are notfixed definitions and the delineation between low flow and high flow canbe anywhere. In this specification low flow is normally used to indicatea flow rate that is lower than a high flow rate and is of a rate that isan acceptable level that does not provide too much discomfort or otherdiscussed disadvantages to a patient when awake. High flow rate can meanany flow rate that is higher than a low flow rate and is not constrainedby the requirement to reduce discomfort or other disadvantages for apatient provided by high flow. It should be noted, that if a flow rateis denoted as “higher” in this specification, that does not necessarilymean it is a high flow rate, but just a flow rate that is higherrelative to another referenced flow rate.

FIG. 5a shows a flow diagram showing the method of operation of thebreathing apparatus that provides flow therapy. The process orcontroller can be programmed to carry out this method. First, thecontroller operates the breathing apparatus to provide a nominal ortypical flow rate when the patient is awake. This flow rate can betermed a “low flow rate”. This flow rate can be set in the usual mannerfor a breathing apparatus of this nature and can be of a suitable rateto provide required therapy while still providing the desired comfortfor the patient and reducing disadvantages of a high flow rate.

For paediatric patients, depending on the ages, 3-5 L/min can beconsidered as high flow and low flow could be any flow rate less than 3L/min. Possible adult patient flow rates were mentioned previously.

The controller operates the breathing apparatus to provide the low flowrate preferably in this range, step 50. At a suitable point, thecontroller then implements the sleep state detection method, step 52.This could occur at any suitable point in the operation of the breathingapparatus, such as time based (periodically, at a particular time), orbased on some physiological or other trigger (such as breathing oranother “preliminary” detection routine for providing an indication ofwhether a patient is awake or asleep). The sleep detection process willbe described below in more detail with reference to FIG. 6. If thecontroller determines that the patient is still awake, then thecontroller continues to operate the apparatus to provide the standard,nominal or low flow rate (low flow mode), step 50. If, however, thecontroller determines that the patient has fallen asleep, step 53, thenit alters operation of the breathing apparatus. For example, theapparatus increases the flow delivered to the target (high) flow rate(high flow mode), step 51. As another example, the apparatus may alsochange the temperature when in sleep mode. This increased flow rate canbe termed a “high flow rate” and can be, for example above 25 litres perminute.

Irrespective of whether the controller maintains the breathing apparatusin the low flow rate mode, step 50, or operates the apparatus in thehigh flow rate mode, step 51, the sleep detection process will becarried out again, step 52, at another suitable point based on thedesired trigger. Therefore, for example, after shifting operation to thehigh flow mode, the controller will detect when a patient awakes again,step 52, and control operation of the breathing apparatus to return itto the low flow mode, step 50. As such, at any time during operation ofthe breathing apparatus it will be operated to provide low flow when thepatient is asleep or high flow (or other change in operation) when thepatient is awake. Clearly, there might be times before the detectionalgorithm operates within a low flow mode even when the patient hasfallen asleep, and likewise stays in a high flow mode even though thepatient has awoken as there could be some lag between changing states.

FIG. 5a shows a typical operation of the device, which commences withthe patient in an awake state and the apparatus providing a nominal/lowflow and then altering the flow to a high rate upon detecting sleep, orretaining the apparatus at the low/nominal flow delivery rate if thepatient remains awake. FIG. 5b shows a more general operation in whichthe apparatus could be in any state (nominal flow or high flow delivery)and the patient could be in any state (a weight/asleep), step 55. Upondetecting a change in sleep state (according for example to FIG. 6),step 56, the flow rate is altered in any suitable manner, step 57,either up or down for either the awake or the sleep state. The shows themore general operation in which upon detecting a change in sleep state,the operation of that apparatus can be altered in any mannerappropriately.

Referring to FIG. 6, the detection process (test mode), step 52, formingpart of the process of FIG. 5a is now described in further detail. Thesleep detection process can be instigated by the controller at anysuitable time during the operation of the breathing apparatus. Forexample, it may be triggered periodically e.g. every 30 minutes, or itmay be triggered based on physiological data from the patient oroperation data from the breathing apparatus. It could alternatively betriggered at certain times of the day. Any other possible triggers couldbe considered by those skilled in the art, and those mentioned shouldnot be considered limiting. A possible trigger will be described furtherlater.

The general process for determining whether a patient is awake or asleepis based on a breathing phenomenon that has been determined by thepresent inventors. When a patient breathes they will have a baselinebreath flow at a baseline flow rate, comprising among other things abreathing (respiratory) rate and signals indicative of tidal volume suchas shown in FIG. 7. The patient will have a (different) baseline breathflow (e.g. respiratory rate and tidal volume) at a particular flow ratewhen they are awake and when they are asleep. FIG. 7 shows the baselinetidal volume when the patient is awake, by way of example, and it willbe appreciated that a similar baseline graph could be produced for whenthe patient is asleep. This baseline breathing flow might be in thepresence of oxygen/air flow provided at a baseline flow rate, such as anominal rate (e.g. 15 Litres/minute) by a breathing apparatus, or at noapplied flow (that is, 0 litres/minute). The baseline breath flowparameters such as respiratory rate and tidal volume can be determinedat any suitable time, such as at a particular flow rate during acalibration routine prior to actual use of the apparatus or at anothertime prior to actual therapeutic use of the apparatus, or the baselinebreath flow parameters could be determined during actual use of theapparatus at the flow rate currently provided by the apparatus at thattime. If the flow rate of air/oxygen delivered to the patient by thebreathing apparatus is increased or higher than the baseline flow rate,the present inventors have determined the following. First, if thepatient is awake, then the respiratory rate (breathing rate)decreases/is lower and the signals indicative of tidal volume inincreases/is higher (compared to the baseline respiratory rate/signalsindicative of tidal volume when the patient is awake.) Alternatively, ifthe patient is asleep, the breathing rate will remain the same (orpossibly decrease slightly) but the signals indicative of tidal volumewill decrease/be lower (compared to the baseline respiratoryrate/signals indicative of tidal volume when the patient is asleep.) Therespiratory rates and signals indicative of tidal volumes can bemeasured by the apparatus using the flow and/or pressure sensors, andthis information processed by the controller. Waveforms (such as that inFIG. 7) show the respiratory rates and signals indicative of tidalvolumes that can be generated from the sensor information. Any one ofthe sensors can be positioned within the apparatus or at/near thepatient interfaces. An arrangement for sensing respiratory rates andtidal volumes is described below.

FIG. 8a (and shown in more detail in FIG. 8c ) shows schematically in atidal volume versus time trace what happens to the respiratory rate andtidal volume of an awake patient compared to the baseline respiratoryrate and tidal volume (of the patient when awake) when the breathingapparatus is controlled to deliver a higher flow rate than the baselineflow rate (in this case a nominal 0 litres/minute). In this case thehigher flow rates are 15 litres per minute, 30 litres per minute and 45litres per minute. As can be seen, at a flow rate higher than thebaseline flow rate in FIG. 7, the respiratory rate is lower/decreases(time between peaks/troughs in the trace increases) and tidal volume ishigher (increases) compared to the baseline respiratory rate and tidalvolume at the baseline flow rate when the patient is awake. Thephenomenon is more pronounced for higher flow rates.

Conversely, FIGS. 8b and FIG. 8d show what happens to the respiratoryrate and tidal volume of an asleep patient compared to the baselinerespiratory rate and tidal volume (when the patient is asleep) when thebreathing apparatus is controlled to deliver a higher flow rate than thebaseline flow rate. As can be seen in FIG. 8b , the flow rate increasesfrom 15 litres per minute (baseline) to 30 litres per minute. At a flowrate higher than the baseline flow rate (transition is approximately atpoint A), the breathing rate stays the same (approximately—that is, thetime between peaks/troughs stays approximately the same) but the tidalvolume is lower (decreases) compared to the baseline respiratory rateand tidal volume at the baseline flow rate. This effect is more visiblein FIG. 8d which shows (when the patient is asleep) the decrease of flowrate (from 15 to 0 L per minute) at point C resulting afterwards in anincrease in tidal volume, and conversely an increase in flow rate atpoint D (from 0 to 15 L per minute) resulting in a decrease in tidalvolume The phenomenon is more pronounced for higher flow rates.

FIGS. 9a to 9f show the decrease in respiratory rate (RR) and increasein tidal volume (VT) demonstrated by an awake patient when the flow ratedelivered by the breathing apparatus is increased to 15 litres perminute, 30 litres per minute and 45 litres per minute respectively overthe baseline flow rate (0 litres/minute in this case) when the patientis awake. FIGS. 10a to 10f show the same phenomenon for when a patientis awake and for when they are asleep. FIG. 14 shows yet furtherschematic examples of other parameters and their change when flow rateincreases, including Tidal volume, minute ventilation (MV) andexpiratory time (TE).

FIGS. 7 to 10 f and 14 show the change in respiratory rate and tidalvolume versus a baseline respiratory rate and tidal volume (at abaseline flow rate) for a particular sleep state when a flow rate isincreased from the baseline flow rate to a higher flow fate. The Figuresare schematic in nature so show trends and not absolute values in allcases. It will be appreciated that the converse phenomenon will beobserved if the baseline flow rate is higher than the changed flow rate.For example, a baseline respiratory rate and tidal volume could bemeasured for a patient (either awake or asleep) at a baseline flow rateof example 15 L per minute, and then the flow rate drop to e.g. 0 L perminute and the respiratory rate and tidal volume measured. If therespiratory rate stays same and the tidal volume increases, it is anindication that the patient is asleep. Conversely, if tidal volumedecreases this can be an indication that the patient is awake. Thisphenomenon (e.g. looking at changes in respiratory rate and/or tidalvolume when flow rate is reduced from a higher baseline flow rate to alower flow rate) could also be used to detect changes in the sleep stateof the patient.

The phenomenon occurs due to the following. Nasal High flow increasesexpiration resistance and decreases inspiration resistance, and itimmediately slows down respiratory rate while the patient is awake.During sleep the change of resistance does not play a role any more andclearing of dead space in the nasal pharynx plays the major role in thephysiological response to nasal high flow. Reduction of dead space evenwithout increase of tidal volume can significantly decrease the deadspace volume (V_(D)) to Tidal volume (V_(T)) ratio and increaseventilatory efficiency. This is the leading mechanism during sleep.During wakefulness, the increase of tidal volume apart from clearingdead space decreases the V_(D)/V_(T) ratio even more significantlyusually followed by a decrease of respiratory rate and as a resultminute ventilation is not changed or is slightly increased. Duringsleep, breathing is shallow and ventilation is more efficient.Increasing flow can jet air into the dead space to flush the dead spaceand produce the phenomenon from which sleep state can be detected.Decreasing flow can provide the opposite effect, which can also be usedto detect sleep states. Providing air via at least one nasal prong ismore desirable, as it is more likely to cause the change in the deadspace which produces the phenomenon, although using a patient interfacewith at least one nasal prong is not necessarily essential. “Dead space”as used herein can refer to both apparatus dead space and anatomicaldead space. Apparatus dead space refers to zones in any additionalequipment such as mask and circuits where the expired gas can bere-breathed again. Anatomical dead space comprises areas in the nose,pharynx, trachea and bronchi where CO₂ levels can build up. The highflow nasal interface can provide improved flushing of the anatomicaldead space.

Based on the determined phenomenon, the controller of the apparatus canbe programmed to carry out the sleep state detection method showngenerally in FIG. 6 to determine whether the patient is awake or asleep.In one sleep state detection embodiment, first, the controller istriggered or receives an internal/external trigger to carry out asleep/wakefulness detection process 59. A baseline respiratory rate andtidal volume is measured for a patient for each of the awake and sleepstates at a baseline flow rate. The baseline respiratory rate and tidalvolume could be measured for a baseline flow rate either beforeoperation of the apparatus during the manufacturing calibration process,or during use of the apparatus at some time prior to conducting thesleep state detection process, step 60. If the baseline breath flowparameters are measured during use of the breathing apparatus, they mayactually be measured on multiple occasions, and the awake state and thesleep state baseline breathing flow parameters might be measured atdifferent times. Where the baseline breath flow parameters are measuredduring use of the breathing apparatus, the baseline flow rate will bethe flow rate being provided by the apparatus at the time ofmeasurement. Baseline measurements are stored where appropriate in thecontroller or other memory of the apparatus. If the baseline breath flowparameters measured during a calibration process prior to use of theapparatus are used, the baseline flow rate can be a suitable nominalflow rate such as 0 litres per minute or alternatively some other lowflow rate. The measurement can take place using e.g. sensors in theapparatus and/or patient interface to measure breath flow such asdescribed below. For this embodiment, the baseline breathing flowparameters are measured during a calibration process at a nominal rate.

The breathing apparatus is then operated to increase the delivered flowrate to a higher (test mode) flow rate, step 61. This could be anysuitable rate higher than the baseline flow rate, e.g. 15, 30 or 45litres per minute or even several different rates could be applied orprovided to the patient and it may not be a high flow rate. For example,if the patient is currently awake, and the apparatus is operating in thelow flow mode, then the increased flow rate will be higher than the lowflow rate (whatever that may be). Alternatively, if the apparatus iscurrently operating in a high flow mode (e.g. on the basis thatpreviously the patient has been determined to be asleep and the flowrate increased accordingly) then the increased flow rate should behigher than that current (high flow mode) flow rate.

The controller then determines from the sensors the respiratory rate andtidal volume of the patient at the increased flow rate. This can be byway of e.g. flow and/or pressure sensors that measure the breath flow ofthe patient through the conduit and/or interface.

The respiratory rate and tidal volume at the elevated flow rate is thencompared to the respiratory rate and tidal volume of the baselinerespiratory rate and tidal volume, step 62. In making the comparison,the appropriate sleep state baseline parameter is selected (namely, theawake baseline or asleep baseline) that can be compared to the currentrespiratory rate and tidal volume in the current sleep state. Possibly,the baseline sleep state parameter for comparison is selected based onwhat the likely current sleep state is. In one alternative, anassumption can be made about the current sleep state or in anotheralternative a preliminary indication of the current sleep state mighthave been received as a result of the trigger determination. In yetanother alternative, the respiratory rate and tidal volume might becompared against the baseline for both the sleep and awake state, if theactual current state cannot be assumed. If the respiratory rate islower/decreases and/or the signals indicative of tidal volume arehigher/increase (e.g. by a threshold value) in each case with respect toa wakefulness sleep state baseline respiratory rate and/or tidal volume,then the controller determines that the patient is still awake, step 63a. Alternatively, if the controller determines that respiratory rate hasstayed the same (or decreased slightly) and/or the tidal volume hasdecreased compared to the asleep baseline respiratory rate and/or tidalvolume, then the controller determines that the patient is asleep, step63 b. The processor then uses this determination in step 53 of FIG. 5ato determine further operation of the device. For example, theinformation is used to vary the flow rate (either up, down or keptconstant) provided by the apparatus accordingly, as for exampledescribed in FIGS. 5a and 5b .

In an alternative to the embodiment above, the flow rate might not beincreased during the sleep state detection process, but rather decreased(or even remain the same). If the detection flow rate is still higherthan the baseline flow rate, then the same phenomenon occurs and thesleep state can be detected by comparing the current respiratory rateand/or tidal volume to the baseline respiratory rate and/or tidalvolume. In an alternative, the respiratory rate and/or signalsindicative of tidal volume at an increased rate could be comparedagainst another reference, such as the respiratory rate and/or tidalvolume of a patient at a particular flow rate when they are known to beawake. Here, sleep might be detected when breathing rate increases (overa slowed awake breathing rate), or expiratory time shortens. Manyalternatives could be conceived also.

The description above relates to control of the apparatus based ondetecting a sleep state by increasing flow rate from a lower flow rateto a higher flow rate and comparing the breath flow parameters tobaseline breath flow parameters. In another sleep state detectionembodiment, the detection of sleep state can be determined using thesame phenomenon, but by decreasing the flow rate from the current flowrate. Referring again to FIG. 6, the alternative embodiment will bedescribed. First, the controller is triggered to carry out asleep/wakefulness detection process 59. A baseline respiratory rate andtidal volume is measured for a patient for each of the awake and sleepstates at a baseline flow rate. The baseline respiratory rate and tidalvolume could be measured for a baseline flow rate before operation ofthe apparatus during the manufacturing calibration process, step 60. Thebreathing apparatus is then operated to decrease the delivered flow rateto a lower (test mode) flow rate, step 61. This could be any suitablerate lower than the baseline flow rate, e.g. 15, 30 or 45 litres perminute or even several different rates could be applied or provided tothe patient and it may not be a low flow rate.

The controller then determines from the sensors the respiratory rate andtidal volume of the patient at the increased flow rate. This can be byway of e.g. flow and/or pressure sensors that measure the breath flow ofthe patient through the conduit and/or interface. The respiratory rateand/or tidal volume at the elevated flow rate are then compared to therespiratory rate and/or tidal volume of the baseline respiratory rateand/or tidal volume, step 62. In making the comparison, the appropriatesleep state baseline breathing parameter is selected (namely, the awakebaseline or asleep baseline) that can be compared to the currentrespiratory rate and tidal volume in the current sleep state. Possibly,the baseline sleep state for comparison is selected based on what thelikely current sleep state is. In one alternative, an assumption can bemade about the current sleep state or in another alternative apreliminary indication of the current sleep state might have beenreceived as a result of the trigger determination. In yet anotheralternative, the respiratory rate and tidal volume might be comparedagainst the baseline for both the sleep in awake state, if the actualcurrent state cannot be assumed. If the respiratory rate is higher orincreases and/or the signals indicative of tidal volume is lower ordecreases (e.g. by a threshold value) in each case with respect to awakefulness sleep state baseline respiratory rate and/or tidal volumethen the controller determines that the patient is still awake, step 63a. Alternatively, if the controller determines that respiratory rate hasstayed the same and/or the tidal volume is higher/has increased comparedto the asleep baseline respiratory rate and/or tidal volume, then thecontroller determines that the patient is asleep, step 63 b. Theprocessor then uses this determination in step 53 of FIG. 5a todetermine further operation of the device. For example, the informationis used to vary the flow rate (either up, down or kept constant)provided by the apparatus accordingly, as for example described in FIGS.5a and 5B.

In an alternative, the respiratory rate and/or signals indicative oftidal volume at an increased rate could be compared against anotherreference, such as the respiratory rate and/or tidal volume of a patientat a particular flow rate when they are known to be awake. Here, sleepmight be detected when breathing rate increases (over a slowed awakebreathing rate), or expiratory time shortens. Many alternatives could beconceived also. In the embodiments described above, a preliminary testcould be carried out to determine an initial indication of the sleepstate and therefore which sleep state (awake or asleep) baselinebreathing flow parameters are used for the comparison. For example, inthe preliminary test, the current respiratory rate and/or tidal volumeare measured and compared against the respiratory rate and/or tidalvolume measured at a previous time. If some change in respiratory rateand/or tidal volume is apparent, then this can provide a preliminaryindication of what the sleep state might be. This can the be used toselect the either the baseline breathing flow parameters for an awakepatient, or the baseline breathing flow parameters for the asleeppatient for comparison to the measured respiratory rate and/or tidalvolume during the sleep state detection method proper, which willconfirm whether or not the preliminary indication is correct.

In yet another sleep state detection embodiment, a similar approach istaken to the two embodiments described above, except the baseline breathflow parameters are determined during actual use of the apparatus.Referring again to FIG. 6, first, the controller is triggered orreceives an internal/external trigger to carry out a sleep/wakefulnessdetection process 59. A baseline respiratory rate and tidal volume isobtained by measuring the current respiratory rate and/or tidal volumeat the current flow rate being provided by the apparatus, step 60. Themeasurement can take place using e.g. sensors in the apparatus tomeasure breath flow such as described below.

The breathing apparatus is then operated to increase the delivered flowrate to a higher (test mode) flow rate, step 61. This could be anysuitable rate higher than the baseline flow rate (which is the previousflow rate prior to increase), e.g. 15, 30 or 45 litres per minute oreven several different rates could be applied or provided to the patientand it may not be a high flow rate.

The controller then determines from the sensors the respiratory rate andtidal volume of the patient at the increased flow rate. This can be byway of e.g. flow and/or pressure sensors that measure the breath flow ofthe patient through the conduit and/or interface. The respiratory rateand/or tidal volume at the elevated flow rate are then compared to therespiratory rate and tidal volume of the baseline respiratory rateand/or tidal volume, step 62 (measured just before flow rate increase).The sleep state of the baseline respiratory breath flow parameters mightnot be known, but this is not essential. If the respiratory rate islower/decreases and/or the signals indicative of tidal volume arehigher/increases (e.g. by a threshold value) in each case with respectto baseline respiratory rate and/or tidal volume, then the controllerdetermines that the patient is still awake, step 63 a. Alternatively, ifthe controller determines that respiratory rate has stayed the sameand/or the tidal volume has decreased/is lower compared to the asleepbaseline respiratory rate and/or tidal volume, then the controllerdetermines that the patient is asleep, step 63 b. If the change inrespiratory rate and/or tidal volume compared to the baselinerespiratory rate and/or tidal volume is inconclusive, the process iscarried out again, path 64. That is, the measured respiratory rateand/or tidal volume at the increased flow rate become the new baselinebreath flow parameters, step 60. The flow rate is then increasedfurther, step 61 and the respiratory rate and/or tidal volume asmeasured at that the further increased flow rate are compared againstthe new baseline breath flow parameters, step 62. Whether the patient isasleep or awake is determined in the same manner as described above,step 63, by looking at the change in current respiratory rate and/ortidal volume versus the baseline respiratory rate and/or tidal volume.This process continues, steps 60-63 and path 64, until there is a changein respiratory rate and/or tidal volume that is conclusive of the sleepstate of the patient—be awake or asleep, step 63 a, 63 b. This periodicor continuous testing and further increasing of the flow rate enablesthe determination of the sleep state to be made, even if the sleep statechanges. For example, if prior to increasing the flow rate the patientis awake and the baseline breath flow parameters are measured, but thenduring the testing process the patient changes state from awake tosleep, the change in parameters might be inconclusive because breathingflow parameters of an asleep state are being compared to the previousbaseline breath flow parameters taken previously when the patient wasawake. However, if the process is continued multiple times, such thatthe current breath flow parameters become the baseline parameters, theflow is increased and then new breath flow parameters measured,eventually the baseline parameters and the current measured breath flowparameters will be for the same sleep state and therefore a conclusivedetermination can be made by comparing them. The processor then usesthis determination in step 53/56 of FIG. 5a or 5 b to determine furtheroperation of the device. For example, the information is used to varythe flow rate (either up, down or kept constant) provided by theapparatus accordingly, as for example described in FIGS. 5a and 5B.

In yet a further sleep state detection embodiment, the process describedabove could be carried out, except that rather than increasing the flowrate during the test, the flow rate is decreased so the flow rate islower than that for the baseline breath flow parameters, step 61. If therespiratory rate is higher or increases and/or the signals indicative oftidal volume are lower or decrease by a threshold value in each casewith respect to the baseline breath flow parameters, then the controllerdetermines that the patient is still awake, step 63 a. Alternatively, ifthe controller determines that respiratory rate has stayed the sameand/or the tidal volume is higher/has increased compared to the baselinerespiratory rate and/or tidal volume, then the controller determinesthat the patient is asleep, step 63 b. If the result is inconclusive,steps 60-63 are repeated via path 64. The processor then uses thisdetermination in step 53 of FIG. 5a to determine further operation ofthe device. For example, the information is used to vary the flow rate(either up, down or kept constant) provided by the apparatusaccordingly, as for example described in FIGS. 5a and 5B.

A possible embodiment of operating a breathing apparatus according tothe general method described with respect to FIGS. 5a, 5b , and 6 is nowdescribed with reference to FIG. 11 which shows one possible sleepdetection process in further detail. First, the process operates thebreathing apparatus to provide a fixed low flow rate to the patient,step 110. At a suitable time (for example when the sleep state detectionmethod is to start) the processor operates the breathing apparatus toincrease the flow rate at a fixed (or optionally variable) rate toprovide a ramp from a low flow rate to a target flow rate, step 111.This could preferably be provided over a fixed period, for example 30minutes. Each increase during the ramp could be considered the increasein flow rate shown in step 61 in FIG. 6.

Periodically or at other suitable times or trigger points, therespiratory rate (RR) and signals indicative of tidal volume (VT) of thebreath flow of the patient at the increased flow rate can be compared tothe baseline respiratory rate and/or tidal volume, step 112. During thecomparison step, the respiratory rate is measured. If the respiratoryrate is slower than the baseline respiratory rate, then this can be afirst indication that the patient is still awake. In addition oralternatively the tidal volume can be measured and compared against thebaseline tidal volume. If this is higher than the baseline tidal volume,then this can be an indication that the patient is still awake. If themeasured respiratory rate is the same as the baseline respiratory rate,then this can be a first indication that the patient is asleep. Inaddition or alternatively the tidal volume can be measured and comparedagainst the selected baseline tidal volume. If this is lower than theselected base line tidal volume, then this can be an indication that thepatient is asleep. The respiratory rate can be measured with a flowsensor and possibly the measurement improved with a flow sensor andpressure sensor. Additionally, a pressure sensor can be used to measuretidal volume. In the alternative, if the respiratory rate remainsunchanged compared to the baseline, then this is an initial indicationthat the patient is now asleep. In addition or alternatively, tidalvolume can be compared against the baseline and if it has decreased,this can be an indication that the patient is asleep.

Therefore, using one or more of the change in respiratory rate and thechange in tidal volume against baseline breathing parameters, the awakeor sleep state can be detected. Various combinations of comparisonscould be used to detect the sleep state. For example, the currentrespiratory rate and tidal volume could be compared against the awakebaseline respiratory rate and tidal volume and also compared against theasleep baseline respiratory rate and tidal volume, and based on therelative differences the sleep or awake state can be determined. It maybe necessary to only use one of these baseline comparisons. Also, itmight not be necessary to use both respiratory rate and tidal volumeparameters, but just one of them. For example if the breathing rateslows with respect to the awake baseline respiratory rate then the awakestate is detected and if it stays the same against the sleep baselinerespiratory rate, then the sleep state is detected (compared to abaseline). Alternatively if the tidal rate increase with respect to theawake baseline tidal volume, an awake state is detected, or if itdecreases compared to the baseline tidal volume, then a sleep state isdetected. Other variations could be conceived.

In an alternative, the respiratory rate would be compared not to thebaseline but to the awake respiratory rate. For example, if uponincreasing flow rate the respiratory rate stays the same with respect tothe baseline, this might mean it actually increases with respect to theawake breathing respiratory rate. Therefore if the respiratory rateincreases upon increased flow, (increased flow delays expiration sousually reduces respiratory rate) this could indicate a sleep state onthe assumption that prior to the increased flow there was an awakestate. Similarly, a decrease in expiratory period over the low volumeflow breathing could be an indication of a sleep state. Many othercombinations and permutations of this are possible. It will beappreciated that it is not necessary for the tidal volume and therespiratory rate to both be considered in determining sleep state.

Once a comparison has been made and a determination has been made thatthe patient is in an awake state (either still or has changed state),then the ramp continues, step 111, and then comparison, step 112, 113occurs again at the next triggered time. (Once a comparison isconducted, the measured respiratory rate and/or tidal volume become thebaseline breathing parameters for the next period detection that iscarried out at the next trigger point.) Alternatively, if a sleep stateis detected, step 113 then the controller operates the breathingapparatus to instigate a second ramp that increases the flow rate at ahigher rate than the first ramp, step 114. This is on the basis that nowthat the patient is asleep, it is desirable to increase the flow rate tothe high rate and to do this as quickly as possible. The increase ispreferably not done as a step change, so as to avoid a change that mightawake the patient or otherwise provide them with discomfort. Thecomparison step can then continue, step 112, to check when the patientawakes again.

The above description is based on the generally assumption thatoperation of the apparatus starts when the patient is wake. This may ormay not be the case. In fact, flow therapy can be provided continuallymeaning there is no defined start point where the patient is awake orasleep. Therefore, it will be apparent to those skilled in the art canrelate to operation of a breathing apparatus at any point in the awakesleep cycle and the apparatus can detect sleep/awake states at any pointand change operation accordingly as necessary.

Further, the above example relates to an apparatus that operates a flowrate ramp at the beginning of therapy—as one possible example. This isnot limiting and is by way of example only. The sleep state detectionmethod could be used to trigger any suitable operation/change inoperation of a breathing apparatus. More generally, at any time ofoperation of the apparatus (either while the patient is awake or asleepand irrespective of whether the apparatus is providing therapeutic orsub-therapeutic flow) the apparatus can detect whether a patient isawake or asleep as described above and then alter the operation of theapparatus according, such as increasing or decreasing or maintaining theflow, either in therapeutic or non-therapeutic modes/flow rates. Oneoption might be to control minute ventilation (MV) in order to achieve areduction work of breathing. A controller would adjust the flow tomaintain minimal MV. The flow setting can be predetermined in the rangeof e.g. 10-35 litres per minute and the controller can adjust flowdepending on calculated MV.

FIGS. 12a to 12c shows some more general operating events by way ofexample. Each figure shows the flow rate provided by the breathingapparatus to a patient and how this varies over time based on variousdetection events. It will be appreciated that the flow rates indicatedare exemplary only and should not be considered limiting.

FIG. 12a shows a first flow rate trace showing various points during theoperation of a breathing apparatus at which the sleep state is detectedand the operation of the breathing apparatus is varied (in this case byvarying of the flow rate provided). The breathing apparatus startsoperation and provides an initial flow rate of 10 litres per minute,which could be sub-therapeutic and is provided while the patient isawake. At point 1, the controller of the breathing apparatus istriggered to carry out the sleep state detection method. The controllerramps up the flow rate and then at point 2 measures the respiratory rateand/or tidal volume of the patient, and then compares this to therelevant baseline respiratory rate and tidal volume of the patient. Inthis example, it is determined that the patient is not yet asleep and sothe breathing apparatus operates to reduce the flow rate down to theinitial flow rate of 10 litres per minute. Some time later, at point 3again the breathing apparatus is triggered to carry out the detectionmethod. It ramps the flow rate to a higher level, and then at point 4measures the respiratory rate and/or tidal volume of the patient andcompares this to the relevant baseline respiratory rate and tidal volumeof the patient. In this example, the apparatus determines that thepatient is now a sleep and ramps the flow rate up to the therapeuticlevel suitable for asleep patient, in this case 20 litres per minute.The apparatus keeps providing a flow rate at this level until it isagain triggered to carry out another sleep state detection at point 5.In this case, when conducting the test, rather than increasing the flowrate further, the controller instead decreases the flow rate. At point 6the respiratory rate and/or tidal volume is measured, and then comparedagainst the relevant baseline respiratory rate and tidal volume. In thisexample, it is determined that the patient is still asleep and the flowrate is therefore returned to the therapeutic flow rate level of 20litres per minute.

This flow rate is provided until the apparatus is again triggered todetermine whether the patient is awake or asleep at point 7. In thiscase, by way of demonstration, the breathing apparatus increases theflow rate to carry out the test. At point 8, it is determined that thepatient is still asleep, so the flow rate is returned to the therapeuticrate of 20 litres per minute and therapy continues. At point 9, theapparatus is again triggered to determine if the patient is awake orasleep, and in this case the flow level is reduced to make thisdetermination. At point 10, the respiratory rate and/or tidal volume ismeasured and compared against the relevant baseline respiratory rate andtidal volume. In this case, it is determined that the patient is nowawake again. As a result, the apparatus is operated to reduce the flowrate down to the sub-therapeutic level of 10 litres per minute, and thebelow that. FIG. 12a shows an example of some of the events that couldoccur during operation of a breathing apparatus that implements a sleepstate detection method as described above and then varies its operationon the basis of the detected sleep state.

FIG. 12b shows a second example of an operation of breathing apparatusthat utilises the detection method. The breathing apparatus initiallyprovides a sub-therapeutic flow rate of 10 litres per minute while thepatient is awake. At point 1 the apparatus is triggered to detectwhether the patient is awake or asleep, and at point 2 it is determinedthat the patient is now asleep using the methods described above. Thebreathing apparatus then ramps the flow rate up to a therapeutic levelof 20 litres per minute, where it continues to provide this level offlow rate until the next detection method trigger point 3. As analternative, shown in dotted lines, the breathing apparatus mightprovide a varied flow rate during this period (between point 2 and point3) as appropriate. This demonstrates that the breathing apparatus afterdetecting the sleep state might carry out alternative flow ratevariations. At point 3, the breathing apparatus is then triggered todetect the sleep state again and lowers the flow rate as part of thatdetection method. At point 4, the breathing apparatus determines thatthe patient remains asleep. It then alters the flow rate in a suitablemanner. Four possible alternatives are shown by way of example in dottedlines. In one alternative, the flow rate is increased again to atherapeutic level, but in this case higher than the previous therapeuticlevel to 25 litres per minute or above. In another alternative, the flowrate is maintained at the flow rate at which the detection method wascarried out—15 litres per minute. In another alternative, the flow rateis reduced back down to or just above the sub-therapeutic initial levelof 10 litres per minute. And in yet another alternative, the flow ratecould be reduced down to a sub-therapeutic level below the initiallevel, such as 5 litres per minute. This figure shows that any variationof flow rate could take place following detection of the particularstate.

FIG. 12c shows another example of a breathing apparatus operation thatimplements the detection method. Again the breathing apparatus operatesto provide a flow rate at an initial level of 15 litres per minute. Atpoint 1 the flow rate is increased and at point 2 the detection methodis carried out to determine if the patient has gone to sleep. Thecontroller determines that the patient has gone to sleep and increasesthe flow rate up to a therapeutic level of 20 litres per minute. It thenvaries the flow rate during this period—which could be for therapeuticreasons. Also, the varying could provide the opportunity to carry outthe detection method as the increase or decrease flow rate can be usedto compare the respiratory rate and tidal volume against a baselinerespiratory rate and/or tidal volume—for example at point 3, 4 and 5.After point 5 it has been determined that the patient has awoken again,at which point the flow rate can be varied in a suitable manner byincreasing, maintaining, or lowering the flow rate as shown in dottedlines.

In the embodiments described above, the detection method takes place byaltering/varying (increasing or decreasing) the flow rate and thencomparing the respiratory rate and/or tidal volume at that varied flowrate to a relevant baseline respiratory rate and/or tidal volume until aconclusive determination is made. In some embodiments, the sleep statedetection method could be carried out at any flow rate, even if it iskept constant. In such a case, the respiratory rate and/or tidal volumeat that constant rate could be compared against the respiratory rateand/or tidal volume for the appropriate sleep state baseline respiratoryrate and/or tidal volume at a different flow rate. Also, in someembodiments the current respiratory rate and/or tidal volume as measuredcould be compared with that for any previous time with a different flowrate provided by the apparatus. For example, as shown in FIG. 12c , atpoint 4, a sleep state detection method could be carried out whereby therespiratory rate and tidal volume at point 4 (e.g. at 25 litres perminute) is compared to that at for example point 2 (e.g. at 15 litresper minute). The respiratory rate and tidal volume at point 2 could beused in lieu of a baseline respiratory rate and tidal volume obtainedduring a calibration process. The sleep state at point 2 is the same asthe sleep state at point 4, the respiratory rate and/or tidal volumecould be compared to that at point 2 to determine whether the patient isawake or asleep.

Many other embodiments of the invention are possible. Any arrangement ofa breathing apparatus that determines sleep state by comparing therespiratory rate and/or tidal volume against a reference (baseline)respiratory rate and/or tidal volume at a reference (baseline) flow ratecould be envisaged. The reference flow rate could be a baseline flowrate in which the respiratory rate and/or tidal volumes are measuredduring a calibration period or similar, or the reference flow rate couldbe at some previous flow rate provided by the breathing apparatus atsome previous point during use of the breathing apparatus.

As previously described, the sleep state detection method is carried outbased on a suitable trigger. One trigger could occur based on apreliminary sleep state detection method. For example, a change inrespiratory rate and/or tidal volume could be determined on from thatand a possible sleep state inferred. On determining a preliminaryindication of sleep state change, the sleep state detection method isthen triggered and could then be used to confirm the preliminarydetection conclusion regarding sleep state.

The embodiments described refer to the use of respiratory rate and/ortidal volume for determining a sleep state. But any suitable breath flowparameter could be used, such a parameters derived from respiratory rateand/or tidal volume. Any embodiments above could utilise such derivedparameters, with the determination of a sleep state being made based onthe change of the derived parameters in a manner that could be envisageby those skilled in the art. Derived parameters could be for example:Minute ventilation (which is respiratory rate×tidal volume), expiratorytime, ratio of inspiratory to expiratory time, ratio of inspiratory timeto total time, ration of expiratory time to total time.

The embodiments above mention varying flow rate appropriately afterdetecting a sleep state. But sleep state detection could trigger otherapparatus operation changes also to improve therapy.

In any of the embodiments described above, the controller operates theblower/fan to provide the required flow rate at any point to conduct thesleep state detection method, and after detection the controlleroperates the blower/fan and any other operations of the apparatus toprovide the required flow, humidity and/or other therapy in accordancewith that required by the sleep state. Operation of a breathingapparatus by a controller will be known to those in the art and is notdescribed in detail here. The controller determines sleep state based onsignals indicative of respiratory rate, tidal volume and/or any otherindicative or derived parameters received from sensors that can measureappropriate parameters to provide such signals.

It will be appreciated that embodiments of the invention can compriseany method or apparatus whereby for a particular sleep state and aparticular flow rate, the respiratory rate and/or tidal volume (orderived parameters) are compared to the same parameters for that sleepstate at a different flow rate, and the change in those parameters canbe used to determine the sleep state. Such a method or apparatus canvary the flow rate, and compare the respiratory rate and/or tidal volumeor other derived parameters to those same parameters prior to varyingthe flow rate and from the comparison determine the sleep state.

What is claimed is:
 1. A high flow therapy apparatus to providehumidified fluid flow to a patient comprising: a housing a flowgenerator in the housing to generate fluid flow, a humidifier tohumidify the fluid flow, a display on the housing, one or more sensorsin the apparatus to measure at least one or both of pressure or flow,and a controller configured to: operate the flow generator and thehumidifier to generate humidified fluid flow at a high flow therapy flowrate to provide to the patient, measure, using the one or more sensors,a breath flow parameter of the patient using the apparatus, the breathflow parameter comprising at least one or both of respiratory rate ortidal volume from a breath flow of the patient, or one or moreparameters derived therefrom.
 2. The high flow therapy apparatus ofclaim 1, wherein the fluid flow is provided via a nasal cannula.
 3. Thehigh flow therapy apparatus of claim 2, wherein the nasal cannula isunsealed.
 4. The high flow therapy apparatus of claim 1, wherein thehumidified fluid flow is provided to the patient via a conduit and thecontroller is further configured to measure the breath flow parameterfrom breath flow of the patient through the conduit.
 5. The high flowtherapy apparatus of claim 4, wherein the breath flow parameter furthercomprises one or both of a respiratory rate or tidal volume.
 6. The highflow therapy apparatus of claim 5, wherein the controller is furtherconfigured to determine the respiratory rate from one or both of theflow rate or pressure of breath flow of the patient through the conduitusing the one or more sensors.
 7. The high flow therapy apparatus ofclaim 1, wherein the controller is further configured to alter operationof the flow generator to increase or decrease the flow rate provided tothe patient based at least on the breath flow parameter.
 8. The highflow therapy apparatus of claim 7, wherein the controller is configuredto alter operation of the flow generator by controlling at least one orboth of speed of a fan in the apparatus or a flow rate of the fluidflow.
 9. The high flow therapy apparatus of claim 1, wherein thecontroller is configured to control operations of the apparatus based ona respiratory rate of the patient.
 10. The high flow therapy apparatusof claim 1, wherein the fluid flow is provided to the patient through anasal cannula with at least one nasal prong to provide air into deadspace of the patient.
 11. The high flow therapy apparatus of claim 1,wherein the flow rate at which the fluid flow is provided to the patientis provided at varying flow rate during a breath cycle.
 12. The highflow therapy apparatus of claim 1, wherein the flow rate at which thefluid flow is provided to the patient is provided at a fixed flow rateduring a breath cycle.
 13. The high flow therapy apparatus of claim 1,wherein the controller is configured to: compare the measured breathflow parameter to an equivalent baseline breath flow parameter of thepatient measured previously at a different baseline flow rate, and alteroperation of the breathing apparatus based on the comparison.
 14. Thehigh flow therapy apparatus of claim 1, wherein in response to thepatient being awake the controller is configured to increase the flowrate to lower the respiratory rate.
 15. A method of controlling a highflow therapy apparatus providing humidified fluid flow to a patient, themethod comprising: operating a flow generator and a humidifier togenerate humidified fluid flow at a high flow therapy flow rate toprovide to the patient, wherein the flow generator is in a housing andconfigured to generate fluid flow, wherein the humidifier is configuredto humidify the fluid flow; and measure, using one or more sensors, abreath flow parameter of the patient using the apparatus, the breathflow parameter comprising at least one or both of respiratory rate ortidal volume from a breath flow of the patient, or one or moreparameters derived therefrom, wherein the one or more sensors are in theapparatus, wherein the one or more sensors are configured to measure atleast one or both of pressure or flow.
 16. The method of claim 15,wherein the humidified fluid flow is provided to the patient via aconduit, and the method further comprising measuring the breath flowparameter from breath flow of the patient through the conduit.
 17. Themethod of claim 16, wherein the breath flow parameter further comprisesone or both of a respiratory rate or tidal volume.
 18. The method ofclaim 17, further comprising determining the respiratory rate from oneor both of the flow rate or pressure of breath flow of the patientthrough the conduit using the one or more sensors.
 19. The method ofclaim 15, further comprising altering operation of the flow generator toincrease or decrease the flow rate provided to the patient based atleast on the breath flow parameter.
 20. The method of claim 19, whereinaltering operation of the flow generation comprises controlling at leastone or both of speed of a fan in the apparatus or a flow rate of thefluid flow.